googleapi/transport: deprecate transport
googleapi/transport: deprecate transport

Fixes #340

Change-Id: I8292d04f727a224833422be7681d5b5407c914c6
Reviewed-on: https://code-review.googlesource.com/c/google-api-go-client/+/49070
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Cody Oss <f11fa1e55ff5638510f5bf86ea76672a630250f9@google.com>

google/google-api-go-client,google/google-api-go-client,googleapis/google-api-go-client,googleapis/google-api-go-client